This invention relates generally to an image forming apparatus, and more particularly to an optical printer or copier in which a latent image formed on a photosensitive medium is pressed against a receiving sheet in order to form an image on the receiving sheet.
Generally, printers and copiers use an electrophotographic or silver halide photographic process to form an image on a photosensitive medium. For example, the electrophotographic process employed in a color copier includes the steps of applying toner powders representing the three primary colors of red, green and blue to a photosensitive drum and then selectively fixing the toner powders on a recording sheet to obtain the desired colored image. The silver halide photographic process includes the steps of forming a latent representation of the image on a photosensitive sheet followed by a visual reproduction of the image through a wet developing process using a liquid developer, a liquid stopper and a liquid fixer. Unfortunately, both the electrophotographic and silver halide photographic processes have several drawbacks.
The electrophotographic process used for copiers generally has poor tonal quality. Color copiers also require a feeding system for the receiving medium with a high degree of precision to prevent the receiving medium from being displaced during its path of travel within the copier. Displacement of the receiving medium, which can result in wrinkling of the receiving medium or jamming of the copier, is due partially to the difficulty in coordinating the timed path of travel of the receiving medium with the timed path of travel of the photosensitive medium. Coordination with the timed path of travel of the photosensitive medium is complicated by the photosensitive medium being repeatedly exposed to optical signals and toner transfer representative of the red, green and blue colored image. Displacement also can occur during the fixing (i.e. heating) of the image on the receiving medium to provide the red, green and blue coloring. Commercially available copiers providing such a high degree of precision in the feeding system for the receiving medium are large in size and costly to manufacture. The tendency of the receiving medium to become displaced during its path of travel within the copier also makes it more difficult to produce a clear, clean colored image on the receiving medium.
The materials used in silver halide photographic processing are not easy to handle due to the wet developing process employed. Silver halide photographic processing also generates an offensive odor and requires disposal of the waste solution and the use of expensive silver halide photographic paper. The silver halide photographic process is a complicated process which increases production costs and requires the use of equipment of large size and weight which is undesirable.
Accordingly, it is desirable to provide an image forming apparatus using a photographic process which produces an image of high tonal quality. The photographic process should also produce clean, clear colored images on the receiving medium, avoid the need to dispose of waste solution, eliminate the generation offensive odors, reduce operating costs and be housed within an apparatus which is smaller in size and weight than presently commercially available.